This is why Burger King's Halloween Whopper completely flopped

Halloween-themed fare at a fast food restaurant seems like a no-brainer. Who wouldn't want to try a seasonal burger at, say, Burger King and enjoy every moment of the spookiest time of year? Well, while Burger King's Halloween Whopper may have been a hotly anticipated item, the excitement surrounding the meal wouldn't last long.

In 2015, FoodBeast reported on how Japanese diners had the opportunity to enjoy black buns at Burger King for years — and it was finally Americans' turn! The limited-time Halloween offering featured a flame-grilled beef patty with American cheese, and topped with lettuce, tomatoes, pickles, onions, mayonnaise, and A.1. Thick and Hearty Sauce. That flavor was echoed in the festive black bun. Sounds yummy right? Maybe it was. But the first problem hopeful tasters encountered: trouble getting the burger at all, as restaurants were sold out (via Twitter).

Then, diners who got to indulge in the $4.99 sandwich quickly learned of a gross side effect from the burger that ultimately led to its downfall.

The black bun on Burger King's Halloween Whopper made diners, well, green

One Twitter user sums up what happened when you ate a Halloween Whopper: "I heard this makes your poop bright green." Yup, the side effect was so common, the hashtag #greenpoop started trending on Twitter (via KDVR News). "Tasted good but my poop is green days later!" another Halloween Whopper taster attested. "More like Halloween disaster! 72 hours later and still not out of my system. And it tasted horrible on top of it all," an angry eater also tweeted. Others claimed it made their bathroom experience blue, not green.

Either way, folks who tried Burger King's Halloween Whopper were not pleased that the chain had not informed them of the potential effects of the food dye used in the bun preparation. Luckily there wasn't necessarily a medical problem to be concerned with, according to Dr. Ian Lustbader, a clinical associate professor of medicine and a gastroenterologist at New York University's Langone Medical Center. "Sometimes stool color is very important, and sometimes we can get worried inappropriately about the color of stool" he explained (via CBS News). But Dr. Lustbader added, "Things like food coloring, done for cosmetic reasons and not the nutritional value of the product, do we really need that?"

In the end, the legacy of the burger was its unpleasant, food dye-related side effect. And needless to say, it won't be back this Halloween.